One of the biggest discoveries of
the last two decades is the fact that we live in
a spatially flat universe whose expansion is
accelerating. This acceleration is consistent
with the effect of a cosmological constant, but
it may also be caused by the presence of a
dynamical energy component with negative
pressure, now termed dark energy (DE), or might
also point to a fundamental modification of our
description of gravity. Dark energy is the
dominant component in the universe,
significantly more important than the barionic
matter, radiation and dark matter. The final
explanation for this component will provide
fundamental knowledge about the nature of
gravity, particle physics and the nature of the
universe as a whole.

As recognized by the Dark Energy Task Force
(DETF): "...We strongly recommend that there be
an aggressive program to explore dark energy as
fully as possible, since it challenges our
understanding offundamental
physical laws and the nature of the cosmos...."
(Albrecht et al. 2006 – Report of the Dark
Energy Task Force,
arxiv.org/abs/astro-ph/0609591.